Anastasia's Relative

Situation puzzles (sometimes called lateral thinking puzzles) are ones where you need to ask lots of yes or no questions to figure out what happened in the situation. These are good puzzles for groups where one person knows the puzzle and answers the questions.

Mrs. Smith had flown all the way from Idaho to sit at this outdoor cafe in Russia and attempt to prove to a duchess that she was the lost princess Anastasia (which she, of course, was not). It seemed to be going well, when the duchess named a member of the former royal family and asked what relation he was to Anastasia. Mrs. Smith froze.
As it so happened, one of her friends was working at the cafe and he had agreed to listen and see if he could help her. He knew the answer, and though he could not talk to Mrs. Smith, write her a note, or make any obvious gestures, he got the message across. Mrs. Smith answered correctly, but later messed up when she agreed to give a blood sample (different puzzle).

Your question is, how did the friend tell Mrs. Smith who the relative was?

Hint

The relative was Anastasia's father.
The friend was not a waiter.
Mrs. Smith knew a little something about music.Hide

Answer

The friend was in the small orchestra playing at the outdoor cafe. Between the pieces, he played three notes that, to anyone else, would sound just like tuning, but Mrs. Smith realized they were D-A-D.Hide